I have encountered this argument before, but I don't really understand it. In short, it seems to go: We are part of nature, so nothing we do can be counted unnatural. So far as I can see, that is a simple fallacy based upon no more than word play (or, perhaps, a confusion between purely descriptive and broadly prescriptive senses of the term "natural"). The kinds of freaky creatures that now populate the landscape around Chernobyl are part of nature, too, but that does not make them "natural". Unlike locusts, human beings can choose what they do to the Earth. They ought to choose wisely. Perhaps you do not share the sentiment, but many people believe that we ought not needlessly drive pandas to extinction not because it is nice for us that there are pandas around but simply because it is a good thing, period, that there are pandas around. This attitude involves a certain kind of resepct for nature that is, it seems to me, difficult to explain and more difficult still to justify. But...